This study presents cross-correlation of building density in outdoor environments for fifth generation mobile communications at 781MHz. To avoid interference from Korean digital television (DTV) broadcasting, the auth...
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This study presents cross-correlation of building density in outdoor environments for fifth generation mobile communications at 781MHz. To avoid interference from Korean digital television (DTV) broadcasting, the authors measured the radio characteristics on Jeju Island using a channel sounder and four-by-four antennas. They derived basic large-scale parameters (LSPs) such as path loss, delay spread, angular spread, and Rician K-factor from eight different sites. The real building standing area was estimated with a geographic information system database. They propose an empirical model from analysis of the correlations between LSPs and building density. This model indicates that building density is not determined by measurement scenario such as urban, suburban, and rural. The proposed model only reflects change in building density for an outdoor environment. Finally, they verify their model through ray-tracing simulation similar to a real environment. This model can be useful in the design of future mobile communications systems according to changes in building density.
An effective approach for the design of spectrum estimation (SE) in cognitive radio systems using multi-taper method (MTM) and spatiotemporal features is presented in this study, whereas the MTM balances the bias-vari...
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An effective approach for the design of spectrum estimation (SE) in cognitive radio systems using multi-taper method (MTM) and spatiotemporal features is presented in this study, whereas the MTM balances the bias-variance dilemma, the multiple-input-multiple-output (MIMO) and space-time block code (STBC) are customarily aimed to defeat the adverse channel effects and enhance the system capacity and performance. The singular value decomposition is exploited to determine the dominant eigenchannels in MIMO and STBC setups. The maximum-ratio combining, on the other hand, is adopted to produce higher signal-to-noise ratios usually intended for high data rates and reliability levels. The statistical analysis and modelling of the performance metrics associated with the SE based on MTM-STBC and MIMO are approached using the quadratic form approximation. Simulation exercises are employed to compare this different SE, which will be called multitaper spectrum estimation (MTSE), against other typical methods such as the periodogram without tapering options. The results exhibit performance gains due to the merger of MTSE and STBC technologies over MIMO and periodogram SE (PSE) algorithms. Further computational analysis shows that the MTSE-STBC has no extra burdens compared with its PSE counterpart.
Linear precoding (LP) techniques for a multiuser multiple-input-multiple-output broadcast channel is investigated and analytical results of the achievable sum capacity and error performance for zero forcing (ZF) linea...
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Linear precoding (LP) techniques for a multiuser multiple-input-multiple-output broadcast channel is investigated and analytical results of the achievable sum capacity and error performance for zero forcing (ZF) linear precoders is presented. It is shown that the detection signal-to-noise ratio of ZF-LP can be accurately approximated by a shrinking Chi-square distribution. The symbol error rate and its achievable diversity gain of ZF-LP are given. Then, an improved linear precoder based on the minimum mean-square error (MMSE) criterion is derived. Its error performance and sum capacity are analysed and compared with that of the ZF-LP. It is shown that the MMSE-LP can achieve much better error performance and a high sum capacity than the existing ZF-LP.
We examine a multiple-inputmultiple-output (MIMO) sampling scheme for a linear time-invariant continuous-time MIMO channel. The input signals are modeled as multiband signals with different spectral supports, and the...
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We examine a multiple-inputmultiple-output (MIMO) sampling scheme for a linear time-invariant continuous-time MIMO channel. The input signals are modeled as multiband signals with different spectral supports, and the channeloutputs are sampled on either uniform or periodic nonuniform sampling sets, with possibly different but commensurate intervals on the different outputs. This scheme encompasses Papoulis' generalized sampling and several nonuniform sampling schemes as special cases. We derive necessary and sufficient conditions on the channel and the sampling rate that allow stable perfect reconstruction of the inputs or, equivalently, perfect inversion of the channel. From an implementation viewpoint, we note that it is desirable that the reconstruction filters have continuous frequency responses. We derive necessary and sufficient conditions that guarantee this continuity property. The frequency responses of the reconstruction filters are specified as solutions to a system of linear equations. Finally, we demonstrate that perfect reconstruction may be possible, even when the channeloutputs are sampled at-an average rate that does not allow the reconstruction of any output from its samples alone. In certain instances, this average rate can achieve the recently presented fundamental bounds on MIMO sampling density.
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